TGF-β1 is the principle growth factor/cytokine involved in radiodermatitis and is produced in abundance by skin fibroblasts, endothelial and keratinocytes upon exposure to radiation.13 Within hours, increased TGF-β1 levels are found in irradiated human, porcine, and mouse skin.13–16 TGF-β1 binds TβRI and TβRII—the transmembrane serine and threonine kinase receptors—which activates the intracellular signaling pathway mediated by the Smad proteins (Fig. 1). The gene discussed is TGFB1; the disease is radiodermatitis.